Azeotropic distillation of chloroethyl benzene from chlorostyrene



Patented May 25, 1948 PATENT OFFICE AZEOTROPIC DISTILLATION OF CHLORO-ETHYL BENZENE FROM CHLOROSTYRENE Lloyd Berg, Bozeman, Mont, and James M.Harrison, Oakmont, Pa., assignors to Gulf Research 81: DevelopmentCompany, Pittsburgh, Pa., a corporation of Delaware No Drawing. Originalapplication December 17,

1945, Serial No. 635,602. Divided and this application May 7, 1947,Serial No. 746,618

8 Claims.

This invention relates to azeotropic distillation, and more particularlyto the separation of chlorostyrene from chloroethylbenzene by theaddition of an entrainer to form an azeotropic system upon distillation.

The search. for plastics suitable for use in synthetic rubberformulation led to the investigation of chlorostyrene as a substitutefor, and an improvement over, styrene in .the butadiene-styrene type ofsynthetic rubber. However, one of the problems arising in chlorostyreneproduction is its separation in a high degree of purity from itsprecursor, chloroethylbenzene. The ordinary distillation oi achloroethylbenzene-chlorostyrene mixture does not produce a satisfactoryseparation in that a low yield of chlorostyrene of the desired highpurity is obtained. This is to be expected in view or the proximity ofthe boiling points of the compounds.

It is an object of this invention, therefore, to separate, bydistillation, monomeric chlorostyrene in a high degree of purity frommixtures containing chloroethylbenzene and chlorostyrene.

It is a further object of this invention to prevent the polymerizationof chlorostyrene in the distillation of mixtures of chlorostyrene andch10- roethylbenzene.

These and other objects are accomplished by the present invention whichincludes adding as an entraining agent methylaceto acetate, butyricacid, benzaldehyde or acetonyl acetone to a mixture containingchloroethylbenzene and chlorostyrene to form. an azeotrope with theohloroethylbenzene and distilling the resultant mixture to remove theazeotrope thereby leaving ohlorostyrene substantially free fromchloroethylbcnzene.

The azeotrope formed by the entrainer and chloroethylbenzene has a lowerboiling point than any or the other components of the charge to bedistilled. Therefore. on distillation, the chloroethylbenzene azeotropewill be vaporized first,

leaving the chlorostyrene substantially free from chloroethylbenzene.

In order to avoid the tendency of the chlorostyrene to polymerize, thefollowing measures have been found effective, either singly or incombinatlon. First, approximately 1 to 2 per cent of a polymerizationinhibitor may be added to the charge to be distilled. Second, it isadvantageous to prevent the temperature of the boiling charge fromexceeding 100 0., and therefore the distillation may-beconducted at areduced pressure. Third, a high-boiling chaser may be added to thecharge. The addition of a high-boiling chaser has the eilect not only ofreducing the 2 formation of polymer, but also of increasing the amountof highly purified chlorostyrene in the overhead distillate from a batchdistillation after the chloroethylbenzene azeotrope has been sepa- 5rated. A chaser is an inert high-boiling liquid which has a boilingpoint considerably greater than either of the compounds to be separated.Suitable chasers are n-cetane and tetradecane.

In separating chlorostyrene from chloroethylbenzene in accordance withthis invention, the amount of entrainer added to the charge to bedistilled is preferably adjusted so as to be approximately equal to theamount required to form an azeotrope with substantially all of thechloroethylbenzene. Less than this amount will result in an incompleteseparation of chloroethylbenzene. More than this amount will result in alower yield of substantially pure chlorostyrene in the bottoms stream.However, it should be understood that this invention is not limited toany specific amount of entrainer. While the addition of an amount ofentrainer approximately equal to the amount required to form anazeotrope with substantially all of the chloroethylbenzene is preferred,variations of this amount will nevertheless result in much greateryields of substantially pure chlorostyrene than can be obtained by thestraight rectification of chloroethylbenzene-chlorostyrene mixtures.

In order. to determine the preferred amount of entrainer to add to thecharge to be distilled, it is necessary to determine the amount ofchloroethylbenzene in such charge. It is also neces sary to determinethe ratio of entrainer to chloroethylbenzene in the azeotrope formed bythe em trainer and the chloroethylbenzene at the desired operatingpressure. From these two factors, the amount of entrainer to add to anymixture of chloroethylbenzene and chlorostyrene fnom which it is desiredto separate the latter in substantially pure form may readily becalculated.

The amount of chloroethylbenzene in admixture with chlorostyrene may bedetermined in any convenient manner known to the art, such as bydetermining the refractive index of the unknown mixture and finding thecomposition corresponding to such refractive index from. a. refractiveindex-composition diagram constructed on from data on mixtures of knowncomposition.

In determining the ratio of entrainer to chloroethylbenzene in theazeotrope formed by the entrainer and the chloroethylbenzene, advantageis taken of the fact that the entrainers of this invention form minimumazeotropes with chloroethylbenzene; that is, the composition at whichthe entrainer and the chloroethylbenzene form a mixture of constantboiling point (the azeotrope) has a lower boiling point than any othermixture of the components or of the individual components separately.Accordingly, to determine the azeotrope for any given entrainer andchloroethylbenzene, it is necessary only to find the composition of theminimum boiling mixture of these components in any known manner, such asby determining the refractive index of the minimum boiling mixture andfinding the composition corresponding to such refractive index from arefractive index-composition diagram constructed from data on mixturesof known composition. The boiling point of the azeotrope and itscomposition will vary according to the pressure at which such boilingpoint is determined. However, at any specified pressure, the boilingpoint and composition of the azeotrope are constant The ratio ofentrainer to chloroethylbenzene in the azeotrope is readily calculatedafter the composition of the azeotrope has been determined.

The product of (a) the ratio of entrainer to chloroethylbenzene in theazeotrope. and (b) the amount of chloroethylbenzene in admixture withchlorostyrene in the charge to be distilled, gives the amount ofentrainer to add to the charge. When the amount of entrainer socalculated is added to the charge, upon distillation, an azeotrope isformed with all of the chloroethylbenzene which is distilled over first,and substantially pure chlorostyrene is left as the residue.

As set forth above, the composition of the azeotrope will vary,according to the pressure at which the boiling point of the azeotrope isdetermined. Any one pressure may be used for determining the compositionof the azeotrope and for the subsequent distillation of the entrainer,chloroethylbenzene, chlorostyrene mixture, provided that the entrainerselected will form an azeotrope with chloroethylbenzene at suchpressure. Therefore, for the distillation, an entrainer is selectedwhich will form an azeotrope with chloroethylbenzene at the desiredpressure. A representative range of pressures for the practice of thisinvention is from about 5 mm. Hg to about 100 mm. Hg.

The following table shows the azeotropic data for the entrainers of thisinvention:

Azeotropic data for entrainers Boiling Point Azeotrope with ChloroofEntrainer, ethylbenzene at 10 O. mm.

Entrainer Boiling Wt. Per Cent 10 Point of Chloro- C. ethylbenzeneMethyl Acetoacetate 171. 7 65.1 60. 0 48. 0 Butyric Acid 163. 7 67. 263. 3 66. 0 Benzalde 179. 0 65. 0 63. 5 43. 0 Acetonyl Acetone 191. 475. 4 66. 0 76.0

isomer of chloroethylbenzene and to any mixture of such isomers. As willbe apparent to one skilled in the art, the azeotropic data for anyspecific isomer or combination of isomers may vary from the data setforth above because of the variation in boiling point of the differentisomers and their various combinations.

A desirable feature of an entrainer is its ready separability from theazeotropic mixture, after the azeotrope has been separated from thechlorostyrene. Separation of the entrainer from its azeotrope withchloroethylbenzene permits the reuse of the latter for conversion tomore chlorostyrene and the reuse of the entrainer to re-form theazeotrope. Methylaceto acetate, acetonyl acetone and butyric acid aresufilclently water soluble to permit their separation from theirazeotropes with chloroethylbenzene simply by extracting with water. Theentrainer may be, recovered from the water extract by distillation at apressure at which the entrainer forms no azeotrope with water.

Alternatively, regardless of the solubility of the entrainer in water,separation of the entrainer from its azeotrope with chloroethylbenzenemay be efiected' by two additional distillations as follows: First, theazeotrope from the original distillation is distilled at a pressuredifferent from the original distillation and adapted to yield a bottomsstream of pure chloroethylbenzene and an overhead stream of an azeotropeof entrainer and chloroethylbenzene in which theentrainer-chloroethylbenzene ratio is higher than in the originalazeotrope. For example, if the original distillation has been conductedat a reduced pressure to avoid polymerization of the chlorostyrene, thefirst additional distillation of the original azeotrope then may beconducted at atmospheric pressure. Second, the entrainerrich azeotropefrom the first additional distillation is then distilled at a pressureadapted to yield a bottoms stream of pure entrainer and an overheadstream of an azeotrope of chloroethylbenzene and entrainer which has alower entrainer-chloroethylbenzene ratio'than the azeotrope formed inthe first additional distillation. For example; if atmospheric pressurehas been used for the first additional distillation, the secondadditional distillation may be conducted at a reduced pressure. The pureentrainer is recycled for use in the original distillation forseparation of chlorostyrene, and the chloroethylbenzene-rich azeotropeis recycled to the first additional distillation.

As another alternative, the original azeotrope of entrainer andchloroethylbenzene may be distilled at a pressure sufliclentl-y high sothat the entrainer no longer forms an azeotrope with thechloroethylbenzene, thus obviating the necessity for a seconddistillation.

The choice of any specific method of recovering entrainer andchloroethylbenzene in practice will depend upon economic considerations.In general, it has been found that the second alternative methoddescribed above is more economical and for that reason is moredesirable.

The following example further illustrates the invention. Unlessotherwise specifically stated, all parts are by weight.

Example.A mixture of chloroethylbenzene and chlorostyrene was found tocontain parts of the former and parts of the latter. Based on the amountof chloroethylbenzene present, 56 parts of butyric acid were addedwhich, upon distillation of the mixture at 10 mm. Hg pressure, formed anazeotrope with all of the chloroethylbenzene. The .mixture wasfractionated in a rectifying column at mm. Hg pressure. The azeotropicmixture of chloroethylbenzene and butyric acid distilled over first,leaving substantially pure chlorostyrene as the residue. Upon furtherdistillation at the same pressure 22.5 per cent of the originalchlorostyrene in a purity of 95 per cent or higher was obtained in theoverhead distillate and 47 per cent remained in the residue. The totalamount of chlorostyrene recovered in a purity of 95-per cent or higherwas 69.5 per cent. Butyric acid was recovered from itschloroethylbenzene azeotrope by'the second alternative method disclosedabove. The first additional distillation was conducted at atmosphericpressure, and the second additional distillation at 10 mm. Hg pressure.

While the above example shows a batch process for the distillation, theadvantages of an azeotropic distillation. in accordance with thisinvention are applicable also to a continuous process. No special typeof apparatus is required,

the conventional batch or continuous stills being satisfactory.

For the purpose of comparing the azeotropic separation of chlorostyrenefrom chloroethylbenzene with the ordinary distillation of mixtures ofthese compounds, the following runs were made. A batch containing 160parts of chloroethylbenzene and 240 parts of chlorostyrene werefractionated in a rectifying column at 10 mm. Hg pressure. Only 35 percent of the original chlorostyrene was recovered from the residue withan apparent purity of 95 per cent or greater. Since the viscosity of theresidue had increased considerably, the separation was probably enhancedby polymerization of the chlorostyrene, so that the value of 35 per centmay be considered a maximum. In an eifort to eliminate the formation ofpolymer and to obtain substantially pure monomeric chlorostyrene in theoverhead distillate, another batch containing 160 parts ofchloroethylbenz'ene, 24.0 parts of chlorostyrene, 3 parts of2,4-dichl0ro-6- nitrophenol as polymerization inhibitor, and 100 partsof n-cetane as a high boiling chaser were fractionated in a rectifyingcolumn at 10 mm. Hg pressure. 95 per cent pure chlorostyrene wasobtained in the overhead distillate and 5.5 per cent remained in theresidue in the still. The amount of substantially 95 per cent purechlorostyrene separated was thus only 14.3 per cent. A comparison of theabove runs with the example of this invention shows the outstandingimprove- 'ment obtained by the method of this invention over a straightrectification.

As has been shown, the use of high-boiling chasers, such as n-cetane andtetradecane, in accordance with this invention, permits recovery of purechlorostyrene in the overhead distillate after all of the azeotrope hasbeen distilled over. Furthermore, the chasers also reduce the tenchencyof the chlorostyrene to polymerize in the still. The use of chasers hasthe efiect, there fore, of increasing the yield of pure monomericchlorostyrene. The amount of chaser to add to the charge to be distilledis not critical. Approximately 1 part of chaser to 2 to 4 parts ofchlorostyrene, chloroethylbenzene mixture may be used. The addition ofapproximately 1 to 2 per cent of a polymerization inhibitor to thecharge to be distilled also reduces the tendency of the chloro- Only 8.8per cent of substantially tilt styrene to polymerize. The use of2,4-dichloro-6- purity than can be obtained by straight rectification.Furthermore, compared with a straight rectification, an azeotropicseparation will reduce, the number of theoretical plates required in thedistilling column; that is, the height of the column and/or the refluxratio are not as great as required for a straight rectification. Theready separability ofv the entralners of this invention from theirazeotropes with chloroethylbenzenehas the advantage of permittingrecovery and reuse of both chloroethylbenzene and entrainer.

The chloroethylbenzene and ehlorostyrene referred to herein havethechlorine substituted in the ring. Accordingly, the termchloroethylbenzene" refers to any of the ortho, meta or para isomers, orto mixtures thereof; and the term chlorostyrene refers to any of theortho, meta or para isomers or to mixtures thereof. The termschloroethylbenzene" and chlorostyrene as used herein include only thosecompounds in which chlorine is substituted in the benzene ring. Thisinvention is applicable to any mixture of chloroethylbenzene andchlorostyrene containing any combination of such isomers,

This application is a division of our application Serial No. 635,602,filed December 17, 1945.

What we claim is:

1. The process of separating chlorostyrene, in which the chlorine issubstituted in the benzene ring, from mixtures thereof withchloroethyibenzene, in which the chlorine is substituted in the benzenering, which comprises adding to a mixture of said chlorostyrene andchloroethylbenzene a member of the group consisting of methylacetoacetate, butyric acid, benzaldehyde and acetonyl acetone to form anazeotrope with the chl'oroethylbenzene upon distillation and subjectingthis mixture to distillation to separate the azeotrope and to leavechlorostyre'ne substantially free from .ohloroethylbenzene.

2. The process of separatingchlorostyrene, in which the chlorine issubstituted in the benzene ring, from mixtures thereof withchloroethylbenzene, in which the chlorine is substituted in the benzenering, which comprises adding to a mixture of said chlorostyrene andchloroethylbenzene a polymerization inhibitor and a member ot the groupconsisting of methylaceto acetate, butyric acid, benzaldehyde andacetonyl acetone to form an azeotrope with the chloroethylbenzene upondistillation and subjecting this mixture to distillation to separate theazeotrope and to leave chlorostyrene substantially free fromchloroethylbenzene. 8. The process of separating chlorostyrene, in whichthe chlorine is substituted in the benzene ring, from mixtures thereofwith chloroethylbenzene, in which the chlorine is substituted in thebenzene ring, which comprises adding to a mixture of said chlorostyreneand chloroethylbenzene a member or the group consisting of methylacetoacetate, butyric acid, benzaldehyde and acetonyl acetone in amountapproximately equal to the amount required to form an azeotrope with thechloroethylbenzene upon distillation and subjecting this mixture todistillation to separate the azeotrope and to leave chlorostyrenesubstantially free from chloroethylbenzene.

4. The process of separating chlorostyrene, in which the chlorine issubstituted in the benzene ring, from mixtures thereof withchloroethylbenzene, in which the chlorine is substituted in the benzenering, which comprises adding to a mixture of said chlorostyrene andchloroethylbenzene a member of the group consisting of methylacetoacetate, butyrlc acid, benzaldehyde and acetonyl acetone to form anazeotrope with the chloroethylbenzene upon distillation, and sub'-'jecting this mixture to distillation at a pressure of from about mm. Hgto about 100 mm. Hg to separate the azeotrope and to leave chlorostyrenesubstantially free from chloroethylbenzene.

5. The process of separating chlorostyrene, in which the chlorine issubstituted in the benzene ring, from mixtures thereof with chloroethylbenzene, in which the chlorine is substituted in the benzene ring, whichcomprises adding to a mixture of said chlorostyrene andchloroethylbenzene an inert liquid having a boiling point higher thanchlorostyrene or chloroethylbenzene at the distillation pressure andalso adding a member of the group consisting of methylacetoacetate,'butyric acid, benzaldehyde and acetonyl acetone to form anazeotrope with the chloroethylbenzene upon distillation and subjectingthis mixture to distillation to separate the azeotrope and to leavechlorostyrene substantially free from chloroethylbenzene.

6. The process of separating chlorostyrene, in

I which the chlorine is substituted in the benzene ring, from mixturesthereof with chloroethylbenzene, in which the chlorine is substituted inthe benzene ring, which comprises adding methylaceto acetate to amixture of said chlorostyrene and ci iloroethylbenzene to form anazeotrope with the chloroethyl benzene upon distillation and subje'ctingthis mixture to distillation to separate the azeotrope and to leavechlorostyrene substantially free from chloroethylbenzene.

7. The process of separating chlorostyrene, in which the chlorine issubstituted in the benzene ring, from mixtures thereof withchloroethylbenzene, in which the chlorine is substituted in the benzenering, which comprises adding butyrlc acid to a mixture of saidchlorostyrene and chloroethylbenzene to form an azeotrope with thechloroethylbenzene upon distillation and subjecting this mixture todistillation to separate the azeotrope and to leave chlorostyrenesubstantially free from chloroethylbenzene.

8. The process of separating chlorostyrene, in which the chlorine issubstituted in the benzene ring, from mixtures thereof withchloroethylbenzene, in which the chlorine is substituted in the benzenering, which comprises adding acetonyl acetone to a mixture of saidchlorostyrene and chloroethylbenzene to form an azeotrope with thechloroethylbenzene upon distillation and subjecting this mixture todistillation to separate the azeotrope and to leave chlorostyrenesubstantially free from chloroethylbenzene.

LLOYD BERG. JAMES M. HARRISON.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS OTHER REFERENCES International Critical Tables,vol. 3, pages 319 and 321. (Copy in Scientific Library.)

Lecat, Annelles des Societe Scientifique de Bruxelles, vol. 49, part 2,pages 291, 292, 313. (Copy in Library of U. S. Geological Survey,Washington, D. C.)

